Measurement properties of the Brazilian version of the Copenhagen Neck Functional Disability Scale in patients with chronic neck pain

Objective To evaluate the measurement properties of the Brazilian version of the Copenhagen Neck Functional Disability Scale (CNFDS) in patients with chronic neck pain. Methods One hundred and five patients were included in the study. The structural validity of the CNFDS was assessed by exploratory and confirmatory factor analysis with the following fit indices: chi-square divided by degrees of freedom (chi-square/df), root mean square error of approximation (RMSEA), comparative fit index (CFI), and Tucker-Lewis index (TLI). To test the construct validity, the CNFDS score was correlated with the Numerical Pain Rating Scale, the Tampa Scale of Kinesiophobia, the Pain-Related Catastrophizing Thoughts Scale, and Neck Disability Index (NDI). A subsample of 43 patients filled the CNFDS at two different times, and test-retest reliability was measured using the intraclass correlation coefficient (ICC), standard error of measurement (SEM), and minimum detectable change (MDC). The internal consistency of the CNFDS was analyzed by Cronbach's alpha. Results CNFDS presented a unidimensional structure, with goodness of fit indices: chi-square/df = 1.37, CFI = 0.94, TLI = 0.93, RMSEA = 0.059. The CNFDS showed satisfactory results of reliability (ICC = 0.93) and internal consistency (Cronbach's alpha = 0.84). The SEM was 1.72 and the MDC was 4.76. The CNFDS showed a high correlation with the NDI (rho = 0.718) and a low correlation with the other instruments. There were no floor and ceiling effects. Conclusion The Brazilian version of the CNFDS with a one-dimensional structure and 15 items has adequate measurement properties.